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<table width="100%" summary="page for M.bahia"><tr><td>M.bahia</td><td style="text-align: right;">R Documentation</td></tr></table>

<h2>Effect of an effluent on the growth of mysid shrimp</h2>

<h3>Description</h3>

<p>Juvenile mysid shrimp (<em>Mysidopsis bahia</em>) were exposed to up to 32% effluent
in a 7-day survival and growth test. The average weight per treatment replicate of
surviving organisms was measured.
</p>


<h3>Usage</h3>

<pre>data(M.bahia)</pre>


<h3>Format</h3>

<p>A data frame with 40 observations on the following 2 variables.
</p>

<dl>
<dt><code>conc</code></dt><dd><p>a numeric vector of effluent concentrations (%)</p>
</dd>
<dt><code>dryweight</code></dt><dd><p>a numeric vector of average dry weights (mg)</p>
</dd>
</dl>



<h3>Details</h3>

<p>The data are analysed in Bruce and Versteeg (1992) using a log-normal 
dose-response model (using the logarithm with base 10).
</p>
<p>At 32% there was complete mortality, and this justifies using a model where a lower asymptote
of 0 is assumed.
</p>


<h3>Source</h3>

<p>Bruce, R. D. and Versteeg, D. J. (1992) A statistical procedure for modeling continuous toxicity data,
<em>Environ. Toxicol. Chem.</em>, <b>11</b>, 1485&ndash;1494.
</p>


<h3>Examples</h3>

<pre>

M.bahia.m1 &lt;- drm(dryweight~conc, data=M.bahia, fct=LN.3())

## Variation increasing
plot(fitted(M.bahia.m1), residuals(M.bahia.m1))

## Using transform-both-sides approach
M.bahia.m2 &lt;- boxcox(M.bahia.m1, method = "anova")
summary(M.bahia.m2)  # logarithm transformation

## Variation roughly constant, but still not a great fit
plot(fitted(M.bahia.m2), residuals(M.bahia.m2))

## Visual comparison of fits
plot(M.bahia.m1, type="all", broken=TRUE)
plot(M.bahia.m2, add=TRUE, type="none", broken=TRUE, lty=2)

ED(M.bahia.m2, c(10,20,50), ci="fls")

## A better fit
M.bahia.m3 &lt;- boxcox(update(M.bahia.m1, fct = LN.4()), method = "anova")
#plot(fitted(M.bahia.m3), residuals(M.bahia.m3))
plot(M.bahia.m3, add=TRUE, type="none", broken=TRUE, lty=3, col=2)
ED(M.bahia.m3, c(10,20,50), ci="fls")

</pre>


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